The advent and widespread adoption of Global Positioning Systems (‘GPS’) in many different types of transport has increased the need for creating and updating geographical information in electronic form.
Modern map-assisted navigation systems rely on the standard GPS technique of sending, from each of a plurality of satellites in geosynchronous orbit about the Earth, usually at least four, successive timing and orbital information signals to a receiver, from which the geographical position, and possibly also a receiver speed and vector are calculated, through trilateration or other technique. The receiver stores electronic map data, which is processed with the GPS data in real time for overlaying the position, speed and vector information thereon or, as the case may be, for scrolling the electronic map data represented on a display relative to a reference point, for instance the vehicle in which the receiver is carried, according to the speed and vector.
The authoring and communication of electronic map data is, in some particular fields of transport, highly regulated. In the field of maritime transport, for example, electronic map data is commonly referred to as Electronic Navigational Charts (‘ENCs’) and must conform to several standards promulgated by the International Hydrographic Organisation (IHO) and the International Maritime Organisation (IMO).
For the specific instance of electronic vector ENCs, notable standards in this field include IHO Special Publication S-57, which specifies ENC data types and formats; IHO Special Publication S-52, which specifies ENC data display formats; and IHO Special Publication S-63, which specifies ENC data encryption and digital signing procedures for purposes of communicating ENC data over networks.
ENCs are frequently updated to reflect changes in sea lane characteristics, which arise from any or all of changing geographical features, for instance a depth modified by gradually-moving sand banks; newly-discovered features or hazards, for instance ship wrecks and other seafloor obstacles; new or updated navigational features, for instance new buoys, lanes and anchoring areas; and new costal features, for instance new seaports, lighthouses, airports, coastal roads and the like. The need to communicate electronic map data is therefore constant, as the above non-exhaustive examples illustrate.
The physical communication of electronic map data can however prove difficult, even in an age of pervasive mobile communications on a global scale. In the same field of maritime transport, ENC and their periodical or ad hoc updates are frequently transmitted by satellite link which, relative to mobile telephony networks for instance, provide much narrower bandwidth across which to perform the communication, moreover made available at a significantly higher cost for the ENC user.
In this context, the International Maritime Organisation (IMO) has recently proposed the compulsory carriage of Electronic Chart Display and Information Systems (ECDIS) making use of ENCs for all existing crafts, which is expected to dramatically increase the requirement for bandwidth to communicate corresponding electronic map data. It would therefore be advantageous to provide vector-based electronic map data that is optimized for communication, in such manner that significantly less bandwidth is required to communicate it, irrespective of the communication network used.